2.1 Sample collection
S. chinensis samples were collected from fresh mature galls on R. chinensis , in Wufeng county (30°10′ N, 110°52′ E, 960 m above sea level), Hubei Province China, on October, 2019. A colony was established through artificial cultivation for further genetic studies. Briefly, autumn migrants ofS. chinensis from mature galls, transferred to a nursery of the moss Plagiomnium maximoviczii , and maintained in a greenhouse. In the following year, nymphs and spring migrants (sexuparae) were harvested from mosses and cultivated in laboratory. Male and female produced by spring migrants were collected in laboratory. After fundatrix emergence, aphids were transferred to host trees for gall induction. Aphid samples were collected separately at different stages, including fundatrix, fundatrigeniae, autumn migrants, overwinter nymphs, spring migrants, male and female sexuales. Fundatrigeniae (females) contained in a gall were transferred to a petri dish after dissecting the gall. Impurities like waxes were removed manually. All aphids within a gall were presumed to be the clonal offspring of a single fundatrix, since all the S. chinensis galls contained only one single fundatrix that produced offspring in the gall via parthenogenesis. All aphid samples were immediately frozen in liquid nitrogen for two hours and subsequently stored at -80°C until further analysis.